De-icing and/or anti-icing of a wind turbine component by vibrating a piezoelectric material

ABSTRACT

A system for de-icing and/or for avoiding an icing of a component of a wind turbine is provided. The system includes a vibrator. The vibrator includes a piezoelectric material and which is adapted to be mounted to at least to a portion of the component, and an electric generator, which is adapted to supply an electric signal to the vibrator, wherein the electric signal causes the vibrator to vibrate and to transfer vibrational energy to at least a surface portion of the component. A corresponding method for de-icing and/or for avoiding an icing of a component of a wind turbine is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of European Patent Office applicationNo. 10162642.2 EP filed May 12, 2010, which is incorporated by referenceherein in its entirety.

FIELD OF INVENTION

The present invention relates to the technical field of wind turbines.In particular, the present invention relates to a system and to a methodfor de-icing and/or for preventing an icing of a component of a windturbine.

ART BACKGROUND

Icing on any exposed part of a wind turbine can occur and causedecreased performance of the wind turbine. Furthermore e.g. when ice isaccumulated on one or more of the rotor blades of a wind turbine, excessvibration problems from uneven blade icing may occur. This in turn maygenerate excessive mechanical loads on the wind turbine componentsleading eventually to wind turbine shut-down or to wind turbine faults.

Problems related to icing can be prevented by at least one of twodifferent measures: A first measure (a) is de-icing, which allows acomponent to ice up before the ice is removed. A second measure (b) isanti-icing which implies prohibiting ice from building up on thecomponent.

Several attempts to come up with equipment and methods for de-icing andanti-icing of wind turbine components have been developed so far:

U.S. Pat. No. 7,217,091 discloses a method for deicing a turbine rotorblade having a blade root, a blade tip, and a leading edge, wherein theturbine rotor blade is coupled to a hub of a turbine. The methodincludes (a) circulating heated air through an outflow channel from theblade root towards the blade tip, (b) re-circulating the heated air viaa return channel from the blade tip to the blade root, whereupon there-circulated heated air becomes returned air, and (c) reheating thereturned air for further circulation.

WO 98/01340 discloses a method for anti-icing or for avoiding an icingof windmill wings of composite materials. Use is made of microwaveenergy for heating the composite material itself. The microwave energyis preferably being supplied from the interior of the windmill wings bymeans of fixedly mounted microwave generators, which are activated inresponse to a detection of occurrence of potential climatic conditionsfor icing.

WO 2009/043352 A2 discloses a method for de-icing a blade of a windturbine, after the wind turbine has been idle for a period of time. Themethod comprises the steps of creating a controlled accelerationcondition of the blade, and subsequently creating a controlleddeceleration condition of the blade, whereby ice is shaken of the blade.

U.S. Pat. No. 6,890,152 B1 discloses a method for de-icing a windturbine blade. The method includes detecting an icy condition on a windturbine blade and causing at least a portion of the wind turbine bladeto vibrate such that ice, which has been built up on the wind turbineblade, breaks off. The vibration may be generated by means of vibratorssuch as commercially available electromagnetic vibrators. For example,the vibrators may be similar to those used in many material conveyorprocesses to shake the sides of bins and other large containers to freeup the product being conveyed. In a particular embodiment, the vibratorsmay be sonic horn that, when being activated, are capable of generatinglow frequency acoustic wave that causes the blade to vibrate. The sonichorns may be located within the blades. Each blade may contain one ormore sonic horns which may be located at or near the leading edge of theblade. The sonic horn(s) may generate an acoustic wave having apredetermined range of frequencies, such as, for example, rangingapproximately from 5 to 500 Hz.

There may be a need for providing an effective de-icing procedure and/orfor an effective anti-icing procedure which can be applied to acomponent of a wind turbine.

SUMMARY OF THE INVENTION

This need may be met by the subject matter according to the independentclaims. Advantageous embodiments of the present invention are describedby the dependent claims.

According to a first aspect of the invention there is provided a systemfor de-icing and/or for avoiding an icing of a component of a windturbine. The provided system comprises (a) a vibrator, which comprises apiezoelectric material and which is adapted to be mounted to at least toa portion of the component, and (b) an electric generator, which isadapted to supply an electric signal to the vibrator, wherein theelectric signal causes the vibrator to vibrate and to transfervibrational energy to at least a surface portion of the component.

The described system is based on the idea that a piezoelectric inducedvibration of a surface portion of the component will ensure, that waterrespectively ice drops cannot “adhere” to the surface of the component.Thereby, an effective anti-icing can be realized. For de-icing purposesthe vibration will ensure that the microscopic adhesions of the icecrystals to the surface of the wind turbine component will be brokenwhich in turn will detach the ice from the wind turbine component.

In this document the term piezoelectric and/or piezoelectricity mayparticularly denote the ability of some materials to generate anelectrical field or electric potential in response to an appliedmechanical stress. The piezoelectric effect is reversible in thatmaterials exhibiting the direct piezoelectric effect i.e. the productionof an electrical potential when stress is applied, also exhibit thereverse piezoelectric effect which is the production of stress (strain)when an electric field is applied.

The piezoelectric vibrator may be embedded within the component,preferably close to the surface of the component. Alternatively, thepiezoelectric vibrator may be attached onto the surface of thecomponent. In this case a top surface of the vibrator represents thesurface of the wind turbine component.

According to an embodiment of the invention the vibrator comprises apiezoelectric film, which is sandwiched between two conductive layers,which are connected to the electric generator. The piezoelectric filmmay be in particular a piezoelectric polymer material. For piezoelectricpolymers such as Polyvinylidene Fluoride (PVDF) and others, intertwinedlong-chain molecules attract and repel each other when an electric fieldis applied resulting in the production of strain.

One or more piezoelectric films may be placed substantially on thesurface of the wind turbine component. The films are electricallyconnected to some alternating current (AC) source. When AC is applied toone or more of the films, the polymer molecules attract and repel eachother and thereby vibrate with a frequency equal to the applied ACfrequency.

The use of a piezoelectric film may provide various advantages comparedto known de-icing and/or anti-icing procedures for wind turbinecomponents: (A) The described de-icing and/or anti-icing system canreact very fast as the desired vibration (attraction and repel of thepolymer molecules) occur immediately when the electric AC is applied tothe films thereby breaking the microscopic attachments between ice andthe turbine component. (B) The described system may be very easy tocontrol i.e. either the piezoelectric films vibrate or they don't. Thisis in substantial contrast to e.g. a heating-up of a wind turbinecomponent from the inside of the component whereby it is necessary toreach a certain temperature at the surface before an ice smelting methodmay work. (C) The described de-icing and/or anti-icing system may allowfor a cost effective de-icing and/or ant-icing procedure e.g. comparedto methods where thermal energy has to be put into a system in order toheat up the whole or parts of the wind turbine component. A furtheradvantage which may be provided by the described system consists of thepossibility, that the de-icing and/or the anti-icing can be easilycontrolled from remote. This may be in particular advantageous if thewind turbine is situated at a location (e.g. within the sea), which isnot or which is not easily accessible. Normally those wind turbines,where icing may become a problem, are located in very remote areas.Therefore, an easy and effective operability by remote control is a veryimportant feature.

According to a further embodiment of the invention the vibrator iscoated with a protective layer. This may provide the advantage that thedurability of the vibrator against environmental influences can besignificantly increased and a long lifetime and a reliable operation ofthe described system can be ensured.

The protective layer may be any material, which ensures that themechanical influence by the piezoelectric film can be transportedthrough the protective layer to the surface of the component and inparticular to the connection surface between the component and theattached ice or the location where the ice may attach.

The protective layer may comprise some elastic or semi-elastic materialsuch as for instance silicone and/or rubber. Further, the protectivelayer may also be a conductive metal foil. Also a conventional coatingor paint could be used for realizing the protective layer.

According to a further embodiment of the invention the vibrator isintegrated within a surface layer of the component. Also this embodimentmay provide the advantage that the durability of the vibrator againstenvironmental influences can be significantly increased and a longlifetime and a reliable operation of the described system can beensured.

Again, it may be important that the surface layer is of a material andcomprises properties that ensure that the mechanical influence by thepiezoelectric film, i.e. the vibrational energy, can be transported tothe surface of the component and especially to the connection surfacebetween the component and the attached ice or where the ice may attach.

In particular if the component is made from a reinforced material, whichcomprises several layers, the piezoelectric film can be easilyintegrated within one layer of reinforced material. When producing sucha component one only has to ensure that also appropriate electric cablesare integrated for applying the electrical signal to the piezoelectricfilm.

According to a further embodiment of the invention the vibratorcomprises a further piezoelectric film, wherein piezoelectric polymerfibers of the piezoelectric film are oriented in a first direction andfurther piezoelectric polymer fibers of the further piezoelectric filmare oriented in a second direction being different to the firstdirection. This may mean that the vibrator of the de-icing and/oranti-icing system is build up of more than one film element, wherein thepiezoelectric polymer fibers of different film elements extend indifferent directions e.g. one section where the polymer molecules areoriented substantially in a longitudinal direction of the component(e.g. a rotor blade) and another section where the polymer molecules areoriented substantially in the transversal direction of the component(e.g. the rotor blade). Thereby, in response to the application of an ACelectric signal each section contracts in different directions. This mayimprove the capability of the vibrator to discard ice which has beenattached to the surface of the component.

According to a further embodiment of the invention the electricgenerator is adapted for generating electric signals having variablefrequencies and/or variable amplitudes. This may provide the advantagethat depending on the structure of the ice, which is supposed to beremoved, an appropriate vibrating frequency and/or an appropriateamplitude can be chosen. Thereby, the amplitude may be defined by thevoltage of the electric signal.

The frequency range, which is covered by the variable frequency waveformgenerator, may extend e.g. from 0.1 Hz up to some kHz, in particularfrom 1 Hz up to 10 kHz and more particular from 20 Hz up to 2 kHz.

In case the vibrator comprises a piezoelectric film as described above,the film thickness may be adapted at least approximately to the intendedfrequency. In other words, the frequency and/or the thickness may bechosen such that the piezoelectric film is driven at least in thevicinity of its resonance frequency. This may provide the advantage thatcomparatively large vibration amplitudes can be realized. Preferably,the resonance frequency may be associated with a thickness modevibration.

Generally speaking, the described electric generator may allow forcomprehensive control possibilities in particular if both the appliedfrequency and the applied voltage can be controlled in numerouscombinations.

Specifically, for various embodiments of the described system, thefrequency of the AC electric signal may be monotonous or may bealternating such as sweeping through a defined frequency spectrum. Forother embodiments the amplitude of the AC electric signal may bemonotonous or may be alternating such as sweeping through a definedamplitude range. Further, the frequency and/or the amplitude of the ACelectric signal may be altered in dependency to one or moreenvironmental parameter such as the temperature, air humidity etc. Inother embodiments the frequency and/or the amplitude of the AC electricsignal may be altered in dependency to one or more operational parametersuch as a vibration in the drive train, rotational speed etc.

According to a further embodiment of the invention the system furthercomprises a sensor, which is connected to the electric generator andwhich is adapted to trigger the operation of the electric generatorbased on a determined environmental and/or operational condition of thewind turbine. This may mean that the described system can initiateitself if the sensor provides an according trigger pulse beingindicative for the occurrence of a predefined environmental and/oroperational condition of the wind turbine. Thereby, such a condition maybe determined by one or by more sensors, which are connected to theelectric generator.

The described sensor(s) may be connected directly to the electricgenerator or indirectly via for instance a control unit to the electricgenerator. Such a control unit may be used for a detailed analysis ofthe sensor signal(s). Thereby, it may be possible that not only theactual sensor output signal(s) is(are) taken into account. A sensorsignal analysis may also take into account a time dependency of therespective sensor output signal(s).

The at least one sensor may be for instance an ice sensor, which isadapted for detecting the presence of ice on the surface of the windturbine component. The at least one ice sensor may be located on anystructure of the wind turbine.

The at least one sensor may also be for instance a sensor, which isadapted for detecting environmental conditions, which might promote aformation of ice on the wind turbine component sensor. In this respectit is mentioned that when specific environmental conditions are met, therisk of icing occurs. However, these conditions are local conditions. Asa wind turbine is stationary, it will be exposed to icing all the timesaid conditions are present. This is in complete contrast to e.g. anairplane (in the air), which is only exposed to the said localconditions as long as the plane flies within this local area. Changinge.g. the altitude of the airplane will change the environmentalconditions and thereby the risk of icing. Therefore an airplane (in theair) can seek to avoid icing, whereas a wind turbine cannot. As aconsequence, the described system with at least one environmental sensormay be very effective for performing a de-icing and/or an anti-icing.Thereby, it is possible to activate the vibrator only when it is reallynecessary. As a consequence, the described system may allow for anenergy efficient de-icing and/or anti-icing.

According to a further embodiment of the invention the vibrator and thesensor are realized with one and the same device. This may provide theadvantage that the described de-icing and/or anti-icing system can berealized with a reduced number of system component parts.

In this respect it may be utilized that a resonance frequency of thevibrator changes when additional mass or inertia is situated on anoscillating portion of the vibrator. Therefore, the above describedpiezoelectric film also may act as a sensor generating a currentdependent on the loads to which the film is exposed. As a consequence,the piezoelectric film may have the function of an ice detector.

According to a further embodiment of the invention the component is ablade of a rotor of the wind turbine. This may provide the advantagethat a wind turbine component can be released from ice and/or can beprotected from the attachment of ice, which component stronglydetermines the efficiency of a wind turbine power generation.

According to a further embodiment of the invention the vibrator coversonly a part of the surface of the blade, in particular a leading edgesurface of the blade. The locations, where the piezoelectric film isplaced, may be preferably locations with the highest risk of icing suchas the leading edge of the blades, anemometers and wind directionsensors.

For various embodiments of the invention, the location where thepiezoelectric film is placed is altered. However, it is of coursepreferable if the piezoelectric film is placed at locations with a highrisk of icing. Such locations are in particular the leading edge of ablade, an anemometer and/or a wind direction sensor.

According to a further embodiment of the invention the piezoelectricmaterial of the vibrator comprises a layout having the shape ofsectioned rectangles. Thereby, the sectioned rectangles may be arrangedalong the leading edge of the blade.

The sectioned rectangles may cover a portion or alternatively at leastsubstantially the full area of the leading edge of the blade. Thepiezoelectric films may be electrically activated individually or incommon.

According to a further embodiment of the invention the piezoelectricmaterial of the vibrator comprises a layout having the shape of aplurality of stripes. The stripes may be arranged along the leading edgeof the blade. Thereby, the stripes may cover a portion or alternativelyat least substantially the full area of the leading edge. Also thestripes may be electrically activated individually or in common.

The control of the various piezoelectric film sections may be dependenton an applied AC control strategy. Thereby, different stripes may beelectrically connected to one or more piezoelectric film sections incommon or separately. The same holds for the above described layouthaving the shape of sectioned rectangles.

According to a further embodiment of the invention the piezoelectricmaterial of the vibrator comprises a layout having the shape of at leasttwo rows of interconnected stripes. Thereby, at least one of the tworows may form a comb-like structure. In case both rows have a comb-likestructure these structures may intervene with respect to each other. Theat least two rows may be electrically activated individually or incommon.

According to a further aspect of the invention there is provided amethod for de-icing and/or for avoiding an icing of a component of awind turbine. The provided method comprises (a) supplying an electricsignal from an electric generator to a vibrator, which comprises apiezoelectric material and which is mounted to at least to a portion ofthe component, (b) vibrating the vibrator in response to the suppliedelectric signal, and (c) transferring vibrational energy from thevibrating vibrator to at least a surface portion of the component.

Also the described method is based on the idea that a piezoelectricinduced vibration of a surface portion of the component will ensure,that water drops cannot “adhere” to the surface of the component suchthat an effective anti-icing can be realized. Accordingly, if ice hasalready been adhered to the component the piezoelectric inducedvibration will ensure that microscopic adhesions of ice crystals to thesurface of the component blade will be broken which in turn will detachthe ice from the component. Thereby, an effective de-icing can berealized.

According to an embodiment of the invention the component is a blade ofa rotor of the wind turbine and supplying the electric signal from theelectric generator to the vibrator is controlled as a function of theactual rotational angle of the wind turbine rotor. This may provide theadvantage that one can control the operation of the vibrator in such amanner that the probability, that ice, which is falling off from a firstblade, cannot hit a second blade, which at the moment of the ice brakeoff, is located below the first blade.

Specifically, it may be possible to activate the vibrator only within atime period, when the respective blade is positioned at leastapproximately below the rotational axis, such that ice, which falls offfrom a large height, can be avoided or the probability of ice fallingdown from a large height can be reduced at least significantly.

In this respect it is mentioned that due to (a) the dimensions of modernwind turbines components, (b) the height of the turbine and (c) thespeed with which the rotor rotate, it may become extremely dangerous ifblocks of ice are loosen from the turbine components and maybe slingaway by e.g. a rotor blade. Therefore, a rotational angle dependingcontrol of the operation of the vibrator may contribute to increase thesafety within a region surrounding the wind turbine.

It has to be noted that embodiments of the invention have been describedwith reference to different subject matters. In particular, someembodiments have been described with reference to method type claimswhereas other embodiments have been described with reference to methodtype claims. However, a person skilled in the art will gather from theabove and the following description that, unless other notified, inaddition to any combination of features belonging to one type of subjectmatter also any combination between features relating to differentsubject matters, in particular between features of the apparatus typeclaims and features of the method type claims is considered as to bedisclosed with this document.

The aspects defined above and further aspects of the present inventionare apparent from the examples of embodiment to be described hereinafterand are explained with reference to the examples of embodiment. Theinvention will be described in more detail hereinafter with reference toexamples of embodiment but to which the invention is not limited.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a wind turbine having a rotor with two blades, wherein eachblade is equipped with a piezoelectric vibrator for de-icing and/or foranti-icing the respective blade.

FIG. 2 shows in accordance with an embodiment of the invention ade-icing and/or anti-icing system for a blade of a wind turbine.

FIG. 3 shows a cross section of a vibrator, which is attached to a windturbine blade and which is covered by a protective layer.

FIGS. 4 a, 4 b and 4 c show various locations for attachingpiezoelectric vibrator(s) onto a rotor blade of a wind turbine.

DETAILED DESCRIPTION

The illustration in the drawing is schematically. It is noted that indifferent figures, similar or identical elements are provided with thesame reference signs or with reference signs, which are different fromthe corresponding reference signs only within the first digit.

FIG. 1 shows a wind turbine 100 according to an embodiment of theinvention. The wind turbine 100 comprises a tower 120, which is mountedon a non-depicted fundament. On top of the tower 120 there is arranged anacelle 122. In between the tower 120 and the nacelle 122 there isprovided a yaw angle adjustment device 121, which is capable of rotatingthe nacelle 122 around a non depicted vertical axis, which is alignedwith the longitudinal extension of the tower 120. By controlling the yawangle adjustment device 121 in an appropriate manner it can be madesure, that during a normal operation of the wind turbine 100 the nacelle122 is always properly aligned with the current wind direction.

The wind turbine 100 further comprises a rotor 110 having three blades114. In the perspective of FIG. 1 only two blades 114 are visible. Therotor 110 is rotatable around a rotational axis 110 a. The blades 114,which are mounted at a driving collar 112, which is also called a hub,extend radial with respect to the rotational axis 110 a.

In between the driving collar 112 and a blade 114 there is respectivelyprovided a blade adjustment device 116 in order to adjust the bladepitch angle of each blade 114 by rotating the respective blade 114around a non depicted axis being aligned substantially parallel with thelongitudinal extension of the respective blade 114. By controlling theblade adjustment device 116 the blade pitch angle of the respectiveblade 114 can be adjusted in such a manner that at least when the windis not so strong a maximum wind power can be retrieved from theavailable wind power.

According to the embodiment described here there is a gear box 124provided within the nacelle 122. The gear box 124 is used to convert thenumber of revolutions of the rotor 110 into a higher number ofrevolutions of a shaft 125, which is coupled in a known manner to agenerator 128. Further, a brake 126 is provided in order to stop theoperation of the wind turbine 100 or to reduce the rotational speed ofthe rotor 110 for instance in case of a very strong wind and/or in caseof an emergency.

The wind turbine 100 further comprises a control system 150 foroperating the wind turbine 100 in a highly efficient manner. Apart fromcontrolling for instance the yaw angle adjustment device 121 thedepicted control system 150 is also used for controlling the rotationalspeed of the rotor 110 by adjusting the blade pitch angle of the rotorblades 114 and by determining an appropriate power generation referencevalue for the wind turbine 100 in an optimized manner. Further, thecontrol system 150 is used for adjusting the yaw angle of the nacelle122 respectively of the rotor 110.

For controlling the operation of the wind turbine 100 the control system150 is connected to a rotational speed sensor 143, which according tothe embodiment described here is connected to the gear box 124. Therotational speed sensor 143 feeds a signal to the control system 150,which is indicative for the current rotational speed of the rotor 110.

Although being not essential for realizing the de-icing and/oranti-icing system, the wind turbine 100 shown in FIG. 1 comprises (a) apower sensor 141 being connected to the generator 128 and (b) anglesensors 142, which, according to the embodiment described here, areconnected to the respective blade adjustment device 116. The powersensor 141 provides information about the current power production ofthe wind turbine 100. The angle sensors 142 provide information aboutthe current blade pitch angle settings of all rotor blades 114.

Further, in accordance with an embodiment of the invention each blade114 comprises an attached piezoelectric vibrator 180, which, when beingin operation, performs an de-icing and/or an anti-icing of therespective surface portion of the respective rotor blade 114. Furtherdetails about the piezoelectric vibrator 180 and the equipment, which iscapable of driving the vibrator 180, are given in the followingparagraphs.

FIG. 2 shows in accordance with an embodiment of the invention ade-icing and/or anti-icing system 260 for a blade 214 of a wind turbine.The system 260 comprises a vibrator 280, which is realized by apiezoelectric film being attached on at least a portion of the surfaceof a wind turbine rotor blade 214. Depending on the specificimplementation the piezoelectric film can cover the whole surface oronly one or more surface portions of the blade 214. Preferably, thepiezoelectric film covers the region of the leading edge of the blade214.

The vibrator 280 is connected via an electric cable 280 a to an electricgenerator 270. The electric cable 280 a, which hereinafter is alsodenominated a vibrator cable 280 a, comprises two wires. A first wire isconnected with a first metallic layer (not depicted in FIG. 2) beingformed at a first surface of the piezoelectric film. The second wire isconnected with a second metallic layer (not depicted in FIG. 2) beingformed at a second surface of the piezoelectric film. By applying anAlternating Current (AC) signal to the two wires the electric generator270 can cause the piezoelectric film to vibrate. The correspondingvibrational energy is then transferred to the surface of the blade 214.The piezoelectric induced vibration of a surface portion of the blade214 will ensure, that water drops cannot “adhere”. Thereby, an effectiveant-icing can be realized. If ice has already been adhered to the bladesurface the piezoelectric induced vibration will ensure that microscopicadhesions of ice crystals to the surface of the component blade will bebroken which in turn will detach the ice from the component. Thereby, aneffective de-icing can be realized.

The de-icing and/or anti-icing system 260 further comprises an icesensor 290, which is connected to the electric generator 270 via asensor cable 290 a. The ice sensor 290 is adapted to trigger theoperation of the electric generator 270 based on a presence of ice onthe blade 214. Therefore, the system 260 can initiate itself if thesensor 290 provides an according trigger pulse being indicative for theoccurrence of the presence of ice. Of course there may also be employedmore than one sensor. Also other sensors than ice sensors may be usedfor instance in order to determine an environmental condition, which inthe absence of vibrations of the vibrator 280 may result in an icing ofthe blade 214.

FIG. 3 shows a cross section of a vibrator 380, which is attached to areinforced material 314 a of a wind turbine blade. The vibratorcomprises a piezoelectric material 384, which is sandwiched between afirst electrode layer 382 and a second electrode layer 386. The twoelectrode layers 382 and 386 form a capacitor, which can be driven withan AC signal being supplied from an electric generator. Thereby, a timedependent electric field will be generated within the piezoelectricmaterial 384, which causes the piezoelectric material 384 to vibrate.The second electrode layer 386 is covered by a protective layer 388,which protects the vibrator 380 from damages which might be caused byrough environmental conditions such as heavy rain or hail.

It is mentioned that the protective layer should be made from amaterial, which allows the vibrations generated by the vibrator 380 tobe transferred to the top surface of the protective layer 388. Thepiezoelectric induced vibrations of the top surface of the protectivelayer 388 will then break the microscopic attachments between ice andthe protective layer 388 such that ice will fall off the rotor blade.

The layout of the piezoelectric film may for various embodiments of theinvention be dependent of parameters such as the location of thepiezoelectric film, the size of the area covered by the piezoelectricfilm, the degree of how exposed the area is, etc.

FIGS. 4 a, 4 b and 4 c show various locations for attachingpiezoelectric vibrator(s) onto a rotor blade 414 of a wind turbine.

FIG. 4 a illustrates a film layout as sectioned rectangles 480 a, whichare arranged along the leading edge of the blade 414 and which coversubstantially the full area of the leading edge. The rectangle films 480a may be electrically activated individually or in common.

FIG. 4 b illustrates a film layout as stripes 480 b along the leadingedge of the blade 414. The stripes 480 b cover only a part of the areaof the leading edge. The stripes may be electrically activatedindividually or in common.

FIG. 4 c illustrates a piezoelectric film layout as two rows 480 c ofinterconnected stripes. The rows 480 c may be electrically activatedindividually or in common.

It should be noted that the term “comprising” does not exclude otherelements or steps and the use of articles “a” or “an” does not exclude aplurality. Also elements described in association with differentembodiments may be combined. It should also be noted that referencesigns in the claims should not be construed as limiting the scope of theclaims.

1.-15. (canceled)
 16. A system for de-icing and/or for avoiding an icingof a component of a wind turbine, the system comprising: a vibrator,which comprises a piezoelectric material and which is adapted to bemounted to a portion of the component; and an electric generator, whichis adapted to supply an electric signal to the vibrator, wherein theelectric signal causes the vibrator to vibrate and to transfervibrational energy to a surface portion of the component.
 17. The systemas claimed in claim 16, wherein the vibrator comprises a firstpiezoelectric film, which is sandwiched between two conductive layers,which are electrically connected to the electric generator.
 18. Thesystem as claimed in claim 17 wherein the piezoelectric film comprises apolymer material.
 19. The system as claimed in claim 16, wherein thevibrator is coated with a protective layer.
 20. The system as claimed inclaim 16, wherein the vibrator is integrated within a surface layer ofthe component.
 21. The system as claimed in claim 16, wherein thevibrator further comprises a second piezoelectric film, and wherein afirst plurality of piezoelectric polymer fibers of the firstpiezoelectric film are oriented in a first direction and a secondplurality of piezoelectric polymer fibers of the second piezoelectricfilm are oriented in a second direction that is different than the firstdirection.
 22. The system as claimed in claim 16, wherein the electricgenerator generates electric signals having variable frequencies and/orvariable amplitudes.
 23. The system as claimed in claim 22, wherein afrequency range extends from 0.1 Hz to 10 kHz.
 24. The system as claimedin claim 23, wherein the frequency range extends from 1 Hz to 10 kHz.25. The system as claimed in claim 24, wherein the frequency rangeextends from 20 Hz to 2 kHz.
 26. The system as claimed in claim 16,further comprising: a sensor, which is connected to the electricgenerator and which is adapted to trigger an operation of the electricgenerator based on a determined environmental and/or operationalcondition of the wind turbine.
 27. The system as claimed in claim 26,wherein the vibrator and the sensor are realized using the same device.28. The system as claimed in claim 26, wherein the component is a bladeof a rotor of the wind turbine.
 29. The system as claimed in claim 28,wherein the vibrator covers only a part of a surface of the blade. 30.The system as claimed in claim 29, wherein the vibrator covers a part ofa leading edge surface of the blade.
 31. The system as claimed in claim27, wherein the piezoelectric material of the vibrator comprises alayout including the shape of sectioned rectangles.
 32. The system asclaimed in claim 27, wherein the piezoelectric material of the vibratorcomprises a layout having the shape of a plurality of stripes.
 33. Thesystem as claimed in claim 27, wherein the piezoelectric material of thevibrator comprises a layout having the shape of at least two rows ofinterconnected stripes.
 34. A method for de-icing and/or for avoiding anicing of a component of a wind turbine, the method comprising: supplyingan electric signal from an electric generator to a vibrator, whichcomprises a piezoelectric material and which is mounted to at least to aportion of the component; vibrating the vibrator in response to thesupplied electric signal; and transferring vibrational energy from thevibrating vibrator to at least a surface portion of the component. 35.The method as claimed in claim 34, wherein the component is a blade of arotor of the wind turbine, and wherein supplying the electric signalfrom the electric generator to the vibrator is controlled as a functionof the actual rotational angle of the wind turbine rotor.